The field of the invention relates generally to display cases, and more specifically, to methods and systems for defogging transparent doors in display cases.
In a transparent door display case, especially a display case that is refrigerated, energy efficiency and consumer product visibility are key. In order to persuade consumers to buy products, the vendors try to make the product visible to the consumer. Fog or condensation accumulated on a transparent door, for example, a door that is at least partially made of glass, may hide the product from the consumer. Hindering the consumer's view of the product may negatively affect the likelihood the consumer will buy the product.
When a transparent door display case has an open door, the evaporator fan tends to blow cold air to the outside of the case and allow warm air into the case. At least one result is that the refrigeration system must work harder to remove this heat and return the inside of the display case to the desired internal temperature. Additionally, if the air transitioned into the display case is of relatively high moisture content, faster icing of the evaporator coils is one possible result. As such, the refrigeration system must incorporate additional defrosting cycles. Defrosting cycles not only use energy, but they also add heat to the system that must be removed by refrigeration cycles.
One current technology for dealing with air exchange between the inside of a display case and the outside environment when a door is opened is an air curtain. One down side of an air curtain, however, is that complicated ductwork is required to generate a proper air curtain, reducing the amount of merchandise space. Providing an air curtain also increases the static loading on the evaporator fan. As such, a higher output motor that consumes more energy is required.
One alternative considered to prevent air exchange is to shut off the evaporator fan motor when the display case door is open. This solution results in additional wear on the motor and related electrical systems due to the constant cycling of motor contactors and motors repeatedly pulling inrush currents in response to the repeated opening and closing of the display case doors. Constantly turning on and off the evaporator fan motors can also create an audible annoyance to the consumer in terms of widely varying air noise.
Most existing technologies for removing fog/condensate from glass require applying heat in some form. Any heat added to the display case system requires the refrigeration system to work that much harder. The refrigeration compressor is the single largest consumer of energy in the display case system. Anti-fog glass can be effective in a wide range of operating conditions, but not all operating conditions. Adding extra airflow across the glass for a short period of time will help the anti-fog glass be more effective in a wider range of conditions. In some display case applications, blowing extra air may be just as effective with regular, lower cost glass as it is with the more expensive anti-fog glass.